1. Field of the Invention
This invention generally relates to electrophotographic scanning of photographic images (photographs and photo transparencies such as 35 mm slides). More particularly, this invention is concerned with the use of desktop scanners capable of scanning either photographs or photo transparencies.
2. Description of Related Art
Desktop scanning units employed to electrophotographically scan sheets of paper bearing printed information usually employ automatic paper feeder mechanisms. Such mechanisms pick individual sheets of paper from a stack and then insert them into the lid of the scanner unit. Upon entering the scanner unit, a given sheet of paper is transported along tightly curved paths to a flat scanning window. After being scanned, the sheet of paper is sent to an output tray. The bending that a sheet of paper undergoes in such scanning units does not, to any unacceptable degree, damage the sheet-like quality of the paper, or the quality of the printing contained thereon.
Thirty five millimeter slides, however, and especially those mounted in cardboard frames, are damaged when they experience severe bending. Moreover, transparencies such as 35 mm slides can not be electrophotographically scanned in the same manner that photographs and sheets of paper are scanned. Transparencies must be scanned with a light source that comes from above the transparency and selectively passes through it. These rays fall upon photodetectors which transduce varying light intensities into varying voltage signals. Conversely, photos and sheets of paper are scanned with a light source whose rays come from below the photo or sheet of paper, impinge on an object contained on the photo or sheet of paper and then are reflected back to a photodetector.
Hence, many users of desktop type scanners are forced to employ three separate and distinct pieces of desktop space-requiring equipment: (1) a paper scanner whose lid has an automatic paper feeder mechanism and a curved sheet transport path, (2) a flatbed scanner for photographs that are loaded into and removed from such scanners by hand and (3) a flatbed scanner for transparencies that are likewise loaded and removed by hand. To some extent this equipment requirement has been alleviated through use of hand operated accessory equipment that provides light (from above) to a single transparency. Such transparency-holding accessories are placed on the window of a electrophotographic scanner whose primary function is to scan sheets of paper bearing printed information. These hand operated devices are (1) limited in the size of the transparency they can handle, (2) not capable of automatically feeding a stack of transparencies into a scanner and (3) tiring to use when several transparencies must be scanned in a relatively short period of time.